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When I installl a 2 stage 15 SEER inplace of a 12 SEER, and drop the cooling bill by 8 to 12 bucks, that is 25% of the cooling bill for many of those homes.

This post, plus an article stating that replacing an econocar with a hybrid really didn't save the much fuel money, inspired me to whip up this spreadsheet.

Assuming I didn't flub the math entirely, they are right- improving on an already efficient (13 SEER or higher) system doesn't save much, because there's not much being spent feeding the 13 SEER to improve upon.

The most dramatic savings are going from a legacy (7 SEER) system to just about anything better. After that, savings are all pretty small, unless you are in equatorial Africa.

But to answer the OP's original question I feel yes 18 seer is overkill, but of course that's just my opinion as you will find many opinions here, personally I think when they went past 10 seer it all went down hill. but you can thank your Daddy Uncle Sam for that move.

I think its overkill for most customers because they neglect some of the other issues effecting their energy bill like windows, insulation, hot attics, undersized ductwork or leaking ducts, insulation, etc.

Yea the really sad thing is that the Government mandated all this higher seer crap so the already filthy rich utilities would not have to build more power plants and left us holding the bag to try and justify to home owners why they need to go with it. I know kw's have went up a lot in the past few years but I am paying more for my electrical bill now then when I had a 10 seer on my home, now I have a 14 seer, go figure. Like someone said here earlier if you are selling your customer comfort then you can walk away from a sale and feel pretty good about it, but if you are selling them on there going to save a ton on the power bill well you your not doing them any favors, matter fact the run time with the higher seer units is longer compared to the lower seer, so if your lucky the power bill will be a wash. I wished they would have just left it a 12 seer being the max and that would have been something we could of all live with, the money we have to charge our customers to install the higher seer systems, is just really hard to justify for us honest folks the have warm blood in our veins, JMO.

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“Experience is a hard teacher because she gives the test first, the lesson afterwards". -Vernon Law-

When sized right, I think the 2-stage should work real well, I was only concerned about oil return in some applications on the low stage, however, the engineers have probably resolved any issue in that regard.

Sized right, the 2-stage should eliminate a big share of run-time-cycles that were not long enough.

Yes, my problem is that I have retired for too long now, & no longer have experience in the field with the new high SEER & the 2-stage systems.

I respect you & those in the field with on hands experience with these units, when you say they get the job done for your customers', I respect your experience with those units.

What is the lowest SEER that you can get the 2-stage in?

Two stage has been around for awhile,no oil return or other issues.IMHO

No problem hrere selling higher SEER,customer are very happy,have a savings and money back gaurantee.

That said most need other things like ductwork corrected as well,and that's part of the savings.Of couurse the contractor needs to capable of detecting this,or it doesn't get corrected or addressed,just ignored!

Warm blooded and secure in our service to consumers here.Many years of doing it the right way the first time.Maybe some skeptics aren't addressing the duct system,or doing a proper install.After all it's two simple gaurantees,how could a consumer go wrong and where else can they get the same,at whatever SEER?

The Real World of A/C Performance

Originally Posted by hangfirew8

This post, plus an article stating that replacing an econocar with a hybrid really didn't save that much fuel money, inspired me to whip up this spreadsheet.

Assuming I didn't flub the math entirely, they are right- improving on an already efficient (13 SEER or higher) system doesn't save much, because there's not much being spent feeding the 13 SEER to improve upon.

The most dramatic savings are going from a legacy (7 SEER) system to just about anything better. After that, savings are all pretty small, unless you are in equatorial Africa.
See attached (I hope). -HF

Your attachment worked okay.
The SEER savings that are presented do not correspond to real world conditions:

SEER - The Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80°F inside and 82°F outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER will not represent the actual seasonal energy efficiency of an air conditioner in your climate and your other environmental and system factors.

The above represents controlled lab test conditions, with only a 2-degree sensible differential between the OAT, using 3 indoor humidity levels.
Are they saying that they manually cycle the A/C on for 6 minutes & off for 24 minutes! How is that a legitimate real world test of efficiency?

Of course, I have always held the same view as Mr. Bill, they should have not outlawed the 10 & 12 SEER units!

Now, they are talking about dropping more of the present SEER levels!
Don't know if my attachment will work?

Your attachment worked okay.
The SEER savings that are presented do not correspond to real world conditions:

No, of course not, because real world conditions are constantly variable, and utterly irreproducible. It would be a huge cooincidence if someone managed to achieve exactly those savings.

It is just a simple mathematical exercise to remind people that, say, 25% savings over a small number is a much smaller savings than 25% savings off of a really big number. It shows that higher SEER ratings save tens of dollars over the middle ratings, where the best values lie, which in turn save hundreds of dollars over legacy equipment.

The sweet spot now seems to be in the 12 (now mandated 13) to 16 SEER, where purchase price is still reasonable as well as the running costs.

Many of your objections to high SEER equipment seem to center around sensible cooling vis a vis humidity removal problems, as well as the cost of long run times; modern variable speed motors, two speed compressors and low speed fan cooling modes address these problems.

MY objection to high SEER equipment is the lack of payback for the inflated cost of the equipment; it simply won't pay back the price premium over its lifetime, which even my non-real-word spreadsheet points out.

Next year, you should put a 13 SEER inplace of your 14, and run it for a year, and then the year after that, install a 15 SEER 2 stage and see how it does.

After all, You need somthing to do with all that money.

If I do that, my wife won't have enough money to get her hair and nails done monthly. We can't have that now, can we?

Seriously, when I was looking to replace my 21 year-old, 7 SEER Trane heat pump, I started trying to do some comparisons between systems. I wasn't as knowledgeable then as I am now (thanks to the kind members of this forum), so I compared compressor RLA of the old system to new systems (this was the only operating data that I was aware of at the time). I decided on a 14 SEER Goodman (one up from the basic builders grade). I got solid numbers with the Goodman: 12 EER, 9 HSPF, full btu's. With MD electric rates jumping 72%, I calculated that my payback would be about 5 years for the new system.

My house is also much easier to heat/cool than many of the homes that I read about. I have a split-foyer, about 1700 sq ft. Good windows and insulation. All-metal ducts, returns in almost every room, no problems with air flow. I am very lucky that I don't have to fight the battles with house construction and air flow that many people have.